Marking pen



FIG. 1 is a perspective view of a marking pen showing my new design;

FIG. 2 is a front elevational view;

FIG. 3 is a left side elevational view, the right side being a mirror image thereof;

FIG. 4 is a rear elevational view;

FIG. 5 is a top plan view; and

FIG. 6 is a bottom plan view thereof. 

The ornamental design for a marking pen, as shown and described. 